Generally, for a material to be suitable for use as an electrical contact, it should be non-fusing with a mating contact material and have a low, ohmic, contact resistance with a relatively small contact pressure. In addition, the material must be capable of maintaining the low resistance after a large number of operations over an extended life period and be corrosion resistant.
Among the contact materials employed in the past are the precious metals such as gold, palladium and platinum and alloys of such metals with each other as well as with metals such as silver and nickel. Due to the high cost of precious metals, a large effort has been employed to find contact materials which are substantially cheaper than the precious metals but which also possess all or many of the properties of the precious metals as mentioned above and, for certain applications, are also solderable.
Marcus et al., in U.S. Pat. No. 4,361,718, have reported the use of nickel-antimony alloy as a contact material over the n-type region of a silicon solar cell. The particular alloy is a 50-50 mixture of nickel and antimony so as to give the compound nickel antimonide and is applied as a powder in the form of a thick film over the solar cell.
We have now discovered that nickel having a surface orientation in a specific crystallographic plane has a much lower contact resistance than ordinary nickel after aging. We have further discovered that such preferred orientation can be induced by doping the nickel with small amounts of specific impurities during electroplating of the nickel.